Patent Literature 1 discloses an example of a conventional power-supply device that supplies an AC current to the induction line.
The power-supply device includes: a DC choke fed with a DC current from the positive output terminal of a DC power supply; a high-frequency transformer including a primary coil having a center tap fed with a DC current through the DC choke and a secondary coil connected to the induction line; a capacitor connected in parallel with both ends of the primary coil of the high-frequency transformer; a first switch connected between one end of the primary coil of the high-frequency transformer and the negative output terminal of the DC power supply; and a second switch connected between the other end of the primary coil of the high-frequency transformer and the negative output terminal of the DC power supply.
The primary coil and the secondary coil of the high-frequency transformer, the induction line, and the capacitor are selected so as to form a resonance circuit resonating at a predetermined frequency. The first switch and the second switch are alternately switched by a switching controller every 180° such that a current passes through the secondary coil at the predetermined frequency. The number of windings on the secondary side of the high-frequency transformer is set at one to increase a current passing through the induction line and minimize the influence of a change of load.
Thus, the high-frequency transformer provides insulation from the DC power supply and supplies a large current of a sinusoidal waveform at the predetermined frequency to the induction line.